Method and apparatus for pest deterrence

ABSTRACT

A pest deterrent device attracts the attention of a pest with ultrasonic noise and then produces a series of flashes to drive off the pest. In one embodiment, the device continuously produces ultrasound, changing the ultrasound when a pest is detected. In another embodiment, the device does not produce ultrasound until a pest is detected. In a further embodiment, the flash charging circuit is used to modulate the ultrasound while the flash is operated. In a particular embodiment, four ultrasonic speakers are arranged in a series-parallel configuration with a total capacitance of about 0.2 micro-Farads achieve 120 dB of sound output with a supply voltage of about 12-18 V.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. pat. application Ser. No.09/844,065 filed 26 Apr. 2001 now U.S. Pat. No. 6,710,705, thedisclosure of which is incorporated by reference.

STATEMENT AS TO THE RIGHTS TO INVENTION MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The present invention relates generally to electronic pest deterrentdevices and more particularly to pest deterrent devices that emitultrasound to drive off animals.

Pests, such as birds, deer, cats, dogs, or rodents among others, cancause significant damage to crops, buildings, stored goods, andlandscaping. A variety of methods and devices have been employed toattempt and reduce the damage caused by pests. Some approaches use ascarecrow or replica of a predator, such as an owl or snake, to scareaway pests. Unfortunately, pests often become accustom to these devicesand they lose their effectiveness.

Other approaches use noise, such as a series of small explosive deviceslinked to a slow-burning fuse, and/or propane guns to scare away pests.Such methods might be inappropriate in an area where the noise would bebothersome. Additionally, the pests or pest might become accustomed tothe repeating noise.

Yet other methods use a detector, such as a motion sensor, to detect thepresence of a pest and trigger a pest deterrent event, such as a noise.Many such detectors work automatically, emitting a loud sound or tonewhen movement is detected. Some pest deterrent devices avoid disruptinghuman activity or comfort by generating just ultrasound, which is beyondthe range of human hearing. However, some pests may still becomeaccustomed to the regular sound, even a fairly loud regular sound.Another issue is that ultrasonic pest deterrent devices can consume afairly large amount of power to produce high levels of ultrasound. Powerconsumption is not much of an issue if a power outlet is available, butbecomes more of an issue if the deterrent device is operating on batterypower. Finally, a user might not be able to tell if the unit is working,i.e. emitting sound, because the sound is above his range of hearing.

Problems associated with power drain can be compounded if the detectorkeeps triggering off of continuous motion of the pest. Similarly, manydetectors, such as passive infrared (“PIR”) or Doppler detectors providelow outputs that must be amplified to turn on relatively high-powerdevices like ultrasound generators. Draw on the power supply and groundcurrent feedback can affect the operation of the detector-amplifiercircuit, causing unreliable triggering.

Accordingly, it is desirable to provide an automatic pest deterrentmethod and apparatus that more effectively drives off pests. It isfurther desirable that the apparatus be efficient to allow operation inremote locations using battery power. It is yet further desirable thatthe user be able to verify that the unit is providing sound.

SUMMARY OF THE INVENTION

An efficient pest deterrent device uses a detector that provides adetection signal to a microprocessor. The microprocessor is used todirectly generate ultrasound, as well as control the operation andtiming of the device. For example, the microprocessor can detect if thedevice is operated on line or battery power, and change device operationto conserve power when the device is battery-operated. The device canthus operate in a variety of modes. On line power, the device alternatesbetween two ultrasonic tones until a pest is detected, at which pointthe devices changes the ultrasonic output to a sweeping output. Theultrasonic sweep can be combined with a flash, preferably delayed fromthe onset of the swept signal by about one second. This delay allows theattention of the pest to be drawn to the ultrasound, and the flash tostartle or otherwise drive off the pest. In a further embodiment, thestrobe charging circuit's oscillator signal can be used to amplitudemodulate (“AM”) the ultrasound to create noisy sidebands from highultrasonic down to within the normal range of human hearing. This AMcreates even more disturbing ultrasound and also allows an operator toconveniently verify sonic output but at much lower sound levels than theultrasound.

In one embodiment, a microprocessor-controlled pest deterrent device hasa passive infrared sensor that produces a train of alternating positiveand negative pulses that are buffered and amplified. The microprocessoris programmed to initiate pest deterrent signals, i.e. activate a load,when an input voltage signal of a selected polarity rises above athreshold level. The load is not active when the input is below thethreshold or of the opposite polarity. The input signal is provided tothe microprocessor by an amplifier and is fed back through a couplingcapacitor as positive feedback to the input of the operationalamplifier, which saturates the operational amplifier. After a selectedperiod of time, the capacitor charges and causes an inverse input signalfed back to the input through the same coupling capacitor, which turnsoff the load after a selected period of time.

The operational amplifier then saturates to the opposite rail. Again,the output is coupled through the coupling capacitor as positivefeedback causing the capacitor to discharge. During this selecteddischarge period, the load is off and the activation circuitry will nottrigger off of a pulse from the sensor or other signal, in other words,the sensor is locked out because the input to the microprocessor is ofthe wrong polarity for activating the load.

In a particular embodiment, the pest deterrent device includes both astrobe light and ultrasonic speakers. When a pest is detected, thedevice either initiates ultrasound or changes the ultrasonic output.After a selected period of time, which can be programmed in themicroprocessor, the strobe is activated and flashes several times for abrief period and then remains off. In one timing sequence, sweepingultrasound is activated when a pest is detected and one second later thestrobe flashes about five times in one half second. The sweepingultrasound remains on for an additional one and one-half seconds, thusthe deterrent event lasts a total of three seconds. The load is thenlocked out for a period of time to avoid continuous triggering or evenself-triggering, such as by the strobe being detected or electronicnoise emulating a triggering event.

In yet another embodiment, a high level of ultrasonic energy is producedby using four ceramic speakers in a series-parallel configuration. Eachspeaker has a nominal input capacitance of about 0.2 micro-Farads, andthe four-speaker series-parallel also has a nominal input capacitance ofabout 0.2 micro-Farads. This is approximately twice the capacitance ofconventional ultrasonic speakers, and achieves a higher peak-to-peakresonant voltage on 12 V battery power or 18 V line power, and over 120dB of ultrasonic power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a pest deterrent apparatusaccording to an embodiment of the present invention;

FIG. 2 is a circuit diagram of a pest deterrent apparatus according toan embodiment of the present invention;

FIG. 3 is a simplified representative time line illustrating a pestdeterrent process according to an embodiment of the present invention;

FIG. 4 is a simplified flow chart of a pest deterrent process accordingto an embodiment of the present invention;

FIG. 5 is a simplified flow chart of a pest deterrent process accordingto another embodiment of the present invention;

FIG. 6 is a simplified flow chart of a triggering process according toan embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an ultrasonic pest deterrent. Variousoperating conditions can be selected depending on the type of powersource available (e.g. line power or battery operation), and theultrasonic deterrent signal can be combined with a flashing light forenhanced deterrent effect. In one embodiment, the ultrasonic signal isinitiated when a pest, such as a deer or dog, is detected. A selectedperiod of time lapses before the flash is discharged, thus ultrasounddraws the attention of the pest in the direction of the device, and theflash startles the pest. In a particular embodiment, the ultrasonicsound is generated with a microprocessor and the low-frequency flashoscillator AM modulates the ultrasound signal to produce sidebands ofultrasonic signal down to some frequencies within the range of normalhuman hearing but at much lower levels. This allows an operator toverify that the device is activated and the speakers are on.

I. An Exemplary Pest Deterrent Device

FIG. 1 is a simplified block diagram of an ultrasonic pest deterrentdevice 10 according to an embodiment of the present invention. A sensor12, such as a passive infrared (“PIR) sensor is aimed at the locationwhere a pest is expected. Alternative sensing devices, such as Dopplerradar devices, could be used. The output of the sensor 12 is provided toa microcontroller 14, which generates the ultrasonic signal that drivesthe speakers 16 and triggers the strobe or flash unit 19, if selected,which includes the bulb 18 and drive circuitry 21. Power to the unit canbe supplied by either batteries 13 or line power 15. The power sourcecan be automatically or manually selected with a switch 11. Line poweris stepped down using conventional power supply techniques.

Sensors typically have low output levels that are amplified withhigh-gain amplifiers 17. These amplifiers can pick up signals that arenot generated by the sensor, such as noise or fluctuations in thevoltage supplied to the sensor or circuit, and trigger device operation.In particular, when the ultrasonic output or strobe is activated, supplyvoltage fluctuations, and ground current feedback can cause unintendedtriggering. A lockout circuit 20 prevents the device from continuouslytriggering if the pest dwells in the target area or if false triggeringevents occur, and allows the amplifiers to settle in anticipation ofanother signal from the sensor.

FIG. 2 is an exemplary circuit diagram for a pest deterrent device 24according to an embodiment of the present invention. Those of skill inthe art will appreciate that many alternative circuits andimplementations of circuit functions are possible. The sensor 12 is adual-element PIR sensor that produces positive and negative pulses onthe output 13 when motion is detected. The PIR is decoupled from theregulated 5 V power IC2 by a 20 k-ohm series resistor R50 and 1000micro-Farad filter capacitor C41.

This decoupling and filtering stabilizes the regulated voltage to thePIR and allows the PIR to function even in the event the batteries areproducing a lowered voltage, even as low as about 3 volts in someinstances. The voltage regulator IC2 provides the unregulated inputvoltage 29 to the output 27 if the input voltage drops below theregulated voltage. There is only about a 0.1 V drop through theregulator, so if the battery voltage drops below about 5.1 volts, thePIR can still function. This is to maintain functions with lowbatteries.

The pulse train from the sensor is inputted to the amplifier IC1C, whichinverts and amplifies the signal. A 0.1 micro-Farad capacitor C16 incombination with a 1 M ohm resistor R27 sets the gain and thelow-frequency bandwidth limit for the detection circuit. The PIR has arelatively low-frequency response, so the amplifier bandwidth is set toabout 0.25-10 Hz. This keeps undesirable higher-frequency signals, suchas might arise from turning a load on or off, from triggering thecircuit.

The output from the first amplifier IC1C drives the second stageamplifier IC1B, which again inverts and further amplifies the signalfrom the PIR and outputs to a comparator IC1A. Though the output of thesecond stage amplifier IC1B swings both positive and negative, only thepositive excursion (which is subsequently inverted in IC1A) is detectedfor triggering purposes. This is achieved according to the programmingof the microcontroller 14, which is programmed to only activate the load(sound and flash) if an appropriate negative voltage is provided to thetrigger input 25. This frees the negative output from IC1B to provide alock-out function. A quad operational amplifier, such as a model LP324M™available from NATIONAL SEMICONDUCTOR is used to implement thecomparators IC1A, and the amplifiers IC1C and IC1B.

When a positive excursion from the second stage amplifier IC1B isdetected, the comparator IC1A swings negative to turn on the load (i.e.to activate the ultrasound and strobe, if selected). This negative swingis fed back through a 2.2 micro-Farad feedback capacitor C20 through aseries resistor R32 to the summing junction 26, which is the negativeinput of the second stage amplifier IC1B. This negative signal providedto the negative input pulls the output of the second stage amplifierIC1B further up towards saturation, providing positive feedback. Thesaturation condition is held until the summing junction voltage iscompensated through the feedback resistor R31 (i.e. until the feedbackcapacitor C20 is sufficiently charged through R31 to pull the secondstage amplifier back from saturation).

After the feedback capacitor C20 is fully charged, the summing junctionreturns to a quiescent state, which switches the output of the secondcomparator IC1A positive. This positive swing is again fed back throughthe feedback capacitor C20 and the series resistor R32 to the summingjunction 26, which causes the output of the second stage amplifier IC1Bto swing to negative saturation because of the positive feedback,essentially disabling the triggering operation. The load is now off andthe second stage amplifier IC1B cannot trigger the load to come on againuntil the feedback capacitor C20 is discharged through the feedbackresistor R31. Thus, the circuit acts as a timer for determining how longtriggering is locked out after the load is turned off, and provides aselected, positive, load on gate, trigger signal to the microcontroller14.

In one embodiment, the time the load is kept on is controlled accordingto the microprocessor programming. In other words, upon receiving atrigger input of the proper polarity, the microcontroller turns on theload for a selected period of time, such as about three seconds. Inanother embodiment, the microcontroller or other circuitry activates theload as long as the trigger signal has the proper polarity and is abovea threshold voltage, for example, as long at the trigger signal is anegative voltage. In one embodiment a three-second-time constant ischosen for the lock out period; however, the lock out period does nothave to equal or even be close to the load-on period. It is generallydesirable that the lock out period hold off the triggering circuit longenough after the load is turned off so that fluctuations in the supplyvoltage, ground potential, or even light from the strobe or othernon-pest input to the sensor, does not create a false trigger. If theload-on period is determined by the duration of the trigger input signal(i e. R31-C20 time constant), a different lock-out period could beobtained by placing a diode and resistor in parallel to each other, theparallel combination being placed in series in the feedback path. Asdescribed above, the output of the second stage amplifier can swing bothpositive and negative, so the feedback capacitor C20 should be anon-polarized capacitor.

The lock out or hold off time after the load goes off insures that thepower supplies and the motion sensor signal amplifiers have all settledbefore motion detection is turned back on. The lock out period alsoeliminates continuous motion detection and extends battery-operatedlifetime. The 10 k-ohm series resistor R32, which is placed close to thesumming junction 26 on the printed circuit board, isolates the summingjunction from noise that might be picked up on the traces between theseries resistor R32 and the trigger input 25. This resistor has littleeffect on timing because it is much smaller than the 470 k-ohm feedbackresistor R31.

The pest deterrent device can operate in a variety of modes. A powerswitch SW1A-SW1D allows the user to select between a high-power mode ora low-power mode. A bayonet plug connector V1 further selects betweenbattery operation or line-voltage operation using an 18 V DC adaptorinput from a 115 V line supply. Plugging in the male bayonet plugautomatically switches out the batteries and provides a control signalto the microprocessor 14 to switch from battery-operated mode to linepower mode.

The unit operates at 100% load duty cycle in high power mode, enablingthe load only when motion is detected (for the 3-second on, 3-secondlockout periods). In high-power battery operated mode, the six-voltbatteries B1, B2 are connected in series to provide twelve volts to thecircuit. When high-power mode is selected and the device is running onbattery power, the unit operates at 100% duty cycle, only enabling theload when motion is detected. In high power mode using the power adaptorfrom line power, the unit continuously emits ultrasound, with a changein the ultrasound when motion is detected. In low-power batteryoperation, the unit operates at 50% duty cycle, with the two batteriesconnected in parallel to provide 6V to the circuit. This improvesbattery lifetime, but produces lower ultrasonic power. The load iscycled on and off at a frequency of about 20 Hz. In low-power operationrunning on line power, the unit operates at 50% duty cycle emitting acontinuous noise, with a change in the ultrasound when motion isdetected.

A sound switch SW3A-SW3C allows selection between a partially audible(to humans) low ultrasonic mode output and a high ultrasonic modeoutput. In low ultrasonic mode on battery power, when motion isdetected, the unit sweeps from 15 kHz to 25 kHz once per second for 3seconds. The sweep is not a continuous sweep, but is carried out in aseries of eight steps. Different sweeps or steps could be used, and thesweep could be generated by an analog circuit in alternativeembodiments. Similarly, the ultrasonic signal could be produced by anexternal oscillator or other device that is controlled by themicrocontroller or other control circuitry.

Experiments with mice were conducted to evaluate the effectiveness of asingle, continuous ultrasonic tone versus the stepwise swept signal.From these observations it is believed that changes in the ultrasonicsignal is a more effective deterrent than a continuous tone. Themicroprocessor 14 is programmed to generate the ultrasonic signaldirectly, which is amplified to drive the speakers. The microcontrollerhas sufficient bandwidth to generate ultrasonic frequencies. In oneembodiment the microcontroller is a custom-masked microcontroller with128 bytes of random access memory (“RAM) using a 4 MHzcrystal-controlled oscillator for the clock. Other types ofmicrocontrollers could be used, such as microcontrollers with integratedflash memory or programmable read-only memory (“PROM”) programmed withthe operating code, or the microcontroller can interface with anexternal memory chip or module that has been programmed to configure themicrocontroller to operate in the desired fashion. Other types of clocksor other clock frequencies compatible with the microcontroller andsufficiently high for direct generation of the highest desiredultrasonic frequency could be used if the microcontroller generates theultrasound.

A flash select switch SW2A turns the flash on or off according to acontrol signal (in this case ground or open) supplied to themicrocontroller. The flash can be enabled in any mode. A 20 kHz flashoscillator 28 charges the 2.2 micro-Farad, 250 V flash capacitor C27 and0.047 micro-Farad 200 V flash trigger capacitor C26 until sufficientvoltage is reached to discharge the strobe tube 30. The strobe flashesfive times in about one half second, according to the time constant ofthe flash trigger capacitor C26 and 3.3 M-ohm series resistor R40. Inlow ultrasonic mode, the flash oscillator is connected to the ultrasonicoutput through a 2 k-ohm series resistor R54 and 0.1 micro-Farad Faradseries capacitor C30, and further modulates the output signal providedto the speakers by modulating the gate voltage of amplifying transistorQ1. The amplitude modulation produces sidebands above and below theultrasonic frequencies being generated and some within the audiblerange. This audible portion of the output can be used to verify that theunit is on and operational. Furthermore, it is believed that the noisegenerated by the amplitude modulation makes the sound emitted by thespeakers more disagreeable to pests, thus improving the effectiveness ofthe pest deterrent.

In low ultrasonic mode on line power, the unit continuously generates asignal switching between 17 kHz and 18 kHz at a rate of about 20 Hz.When motion is detected, the unit step-wise sweeps from 15 kHz to 25 kHzonce a second for about 3 seconds. After the 3-second sweep period, theunit returns to the quiescent state of alternating between 17 kHz and 18kHz at a rate of 20 Hz until another trigger from the sensor enables theload (i.e. another triggering event after the lock-out period).

In high ultrasonic mode running on batteries, the unit sweeps from about25 kHz to 40 kHz once per second for three seconds. Some animals do notrespond to the high end of this range, and in other embodiments, theunit steps from 24-25 kHz, or 20-30 kHz. Other ranges and step sizes maybe selected. In another embodiment, using line power, the unitcontinuously generates a signal switching between 31 kHz and 32 kHzuntil motion is detected. When motion is detected, the unit sweeps from25 kHz to 38 kHz (or other range) for three seconds, and then returns toalternating between 31 kHz and 32 kHz.

II. Operation of the Flash Circuit and Duty Cycle

When the flash is selected, the strobe flashes five times for half asecond starting one second after motion is detected. Thus, as soon asmotion is detected the ultrasonic signal is generated or changes from aquiescent state (e.g. alternating 17/18 kHz or 31/32 kHz), but the flashdoes not strobe until the sound has been on for about one second. Thisprovides an opportunity for the pest to direct its attention at thedevice before the flash comes on. It is believed that this combinationof sound and flashing light with an intervening period is a moreeffective deterrent than if the flash started concurrently with thesound because the pest would not have an opportunity to look at thedevice before the flash started.

If the unit is in low ultrasound mode, a further advantage is obtainedfrom the amplitude modulation of the low ultrasound signal by the flashoscillator. Namely, when the flash oscillator is enabled, an additionalchange in the sound output occurs as the AM sidebands are produced. Thisproduces a very disturbing sound from as low as about 4 kHz to over 30kHz that occurs during, and as a function of, strobing.

The flash oscillator transistor Q7 uses feedback from the transformerXF1. The high voltage output of the transformer XF1 is rectified by thediode D5 and charges the flash capacitor C27. As the flash capacitorcharges, the flash trigger capacitor C26 also charges through theresistor R40. The flash trigger capacitor C26 is in series with thetrigger transformer L1. When the voltage at the cathode K of theprogrammable uni-junction transistor (“PUT”) 32 drops low enough, thePUT turns on, discharging the series capacitor C26 through the triggertransformer L1. This current creates the trigger voltage to fire theflash and discharge the flash capacitor C27 through the strobe tube 30.The flash capacitor C27 immediately starts re-charging, and the cyclestarts over with the resistor R40 and series capacitor C26 controllingthe flash strobing rate. The flash oscillator 28 is turned on and off bythe microcontroller 14 through a flash control line 31.

When low-power operation is selected, the microcontroller 14 generates alow-frequency square wave at the duty cycle output 34 to drive a bipolartransistor Q2 on and off. This transistor is in series with theultrasonic output 36 of the microcontroller and the output amplifier Q1.The edges of the square wave are rolled off by 1 k-ohm resistors R71,R72 in series with the base of Q1, and the 1 micro-Farad capacitor C44connected between a center node 38 of the resistors and ground 40. Thesquare wave edges are rolled off to prevent clicking in the speakers asthe ultra sound is gated on and off.

III. Output Driver and Speakers

The output amplifier Q1 is turned on and off by the ultrasonic output 36from the microcontroller 14. External resistors R23, R24 allow changingthe high and low frequencies generated by the microcontroller withouthaving to re-program the microcontroller. The tapped inductor L2 forms aresonant circuit with the speakers SP1, SP2, SP3, and SP4 to ring themwith a sine wave. The speakers are bi-morph ceramic speakers with afrequency response from about 4 kHz up to about 40 kHz and are connectedin series-parallel. In other words, two sets of two parallel speakersare connected in series. In the low range, the speakers are connectedacross the entire center-tap inductor L2, while in the high range thespeakers are connected to the tap 42 of the inductor L2 for a lowerinductance. The switch SW3A, SW3B is a mechanical two-position switch,but electronic switching of the inductance could be done to broaden therange of frequency sweeping using several inductors and taps, orvariably-tunable inductors could be used.

By connecting the speakers in a series-parallel configuration higheroutput power is achieved. Each speaker has a capacitance of about 0.2micro-Farads, which is twice the capacitance used in a conventionalultrasonic speakers that typically have a capacitance of about 0.05-0.1micro-Farads. The series-parallel arrangement of the speakers provides acombined capacitance of 0.2 micro-Farads. This allows more current drawand more power to be drawn by the speakers, and more sonic power to bedirected at the pest. Similarly, while most speakers in conventionalultrasonic pest deterrent devices are driven at about 20V peak-to-peak,producing about 90-100 dB total sonic power, the present circuit,utilizing a combined total 0.2 micro-Farad speaker load and achievingabout 50 V peak-to-peak when in resonance with L1, produced over 120 dB.In another embodiment, the total ultrasonic output level was over about110 dB.

The ultrasonic output of a unit fabricated according to the presentinvention generated over 120 dB measured 18 inches from the speakers atsame ultrasonic frequencies. Not all the ultrasonic power could befocused on the point of measurement, so it is believed that the actualultrasonic output power is well over 120 dB. Using either a 12 V batteryor 18 V line source also increases the power available to the speakersover conventional 6 V or 12 V designs.

IV. An Exemplary Timeline and Methods

FIG. 3 is a representative timeline illustrating the operation of a pestdeterrent device with the flash enabled according to an embodiment ofthe present invention. The sensor detects the presence of a pest at T0and generates a series of alternating positive and negative pulses.Essentially instantaneously the ultrasound is turned on, if originallyoff, or changed to a sweep from an alternating tone, depending on themode of operation. After one second T1, the flash flashes for aboutone-half second until T2, which is at 1.5 seconds. The sweepingultrasound remains on for an additional 1.5 seconds (three secondstotal) until T3. The sensor is than locked out of triggering the loadfor a period of about 2.5 seconds, allowing the trigger sensingamplifiers to settle after the load(s) is turned off, until T4, whichoccurs at 5.5 seconds. After the lock-out period the cycle can re-startif the sensor detects another or the same pest. These times are merelyexemplary.

FIG. 4 is a simplified flow chart of a pest deterrent process 400according to an embodiment of the present invention. A sensor generatesa pest detection signal (step 402) that initiates an ultrasonic signal(step 404) at a pest deterrent unit. After waiting a selected period oftime (step 406), for example about 1 second, a light flash(es) isgenerated (step 408) at the pest deterrent unit. In a further embodimentthe ultrasonic signal is amplitude modulated by the flash oscillatorsignal during the period the light is flashing (step 410). It isintended that the ultrasonic signal attracts the attention of the pestto the pest deterrent unit, and that the flash then startles the pest todrive it away.

FIG. 5 is a simplified flow chart of a pest deterrent process 500according to another embodiment of the present invention. A pestdeterrent unit produces a first ultrasonic output prior to motion beingdetected (step 502). For example, the unit could produce a continuoustone or alternating high-low tones. When motion is detected (step 504),the unit changes to a second ultrasonic output (step 506), such as aswept (frequency) ultrasonic signal, amplitude modulated ultrasonicsignal, or chopped (on/off) ultrasonic signal.

FIG. 6 is a simplified flow chart of a signal triggering process 600according to another embodiment of the present invention. When movementoccurs within the range of a motion sensor, the sensor generates atrigger signal having a first polarity (i.e. positive or negative) (step602). The trigger signal is provided to a saturating amplifier (step604) capable of producing a positive or a negative output voltage and aload is activated (step 606). Positive feedback is provided to thesaturating amplifier to drive the amplifier to a first saturationvoltage (step 608). Positive feedback from the first saturation voltageis provided through an inverter and a feedback capacitor to a summingjunction input of the saturating amplifier and negative feedback fromthe output of the saturating amplifier is provided to the summingjunction through a feedback resistor (step 610), which discharges thefeedback capacitor at a first selected rate.

After a selected period of time, the voltage at the summing junctiondrops below a first threshold voltage and the saturating amplifierprovides a second saturation voltage having the opposite polarity fromthe first saturation voltage (step 612). The load, which is only enabledif a signal with the first polarity is detected, is de-activated (step614). Positive feedback from the second saturation voltage is providedthrough the inverter and the feedback capacitor to the summing junctioninput of the saturating amplifier, and negative feedback is providedfrom the output of the saturation amplifier to the summing junctioninput through the feedback resistor to discharge the feedback capacitorat a second selected rate (step 616), wherein a second trigger signalwill not activate the load until after the load is de-activated and thevoltage at the summing junction drops below a second threshold voltage.The term “below” relates to the absolute value of the voltage(s) at thesumming junction.

The rate of compensation in one embodiment is essentially equal, thatis, the high and low saturation voltages have about the same magnitudeand only a feedback resistor is used to couple negative feedback to thesumming junction. In an alternative embodiment, the saturation voltagesmight not be symmetrical, and in yet other embodiments, a diode (ordiode with a series resistor) can be placed in parallel between theoutput of the saturating amplifier and the summing junction.

Although the present invention has been described with reference tospecific embodiments, modification and variation can be made withoutdeparting from the subject of the invention as defined in the followingclaims. For example, a sound detector, vibration detector, or radardetector might be used instead of a PIR as the pest detector. Further,the load, although described in specific embodiments as aseries-parallel combination of high-capacitance ceramic speakers couldbe other types of speakers or ultrasonic devices. Similarly, althoughspecific circuits with specific values of components have beendescribed, other circuits, component values, and types of devices couldbe used, such as by using analog circuits to provide some of thefunctionality of the microprocessor in certain embodiments.

1. A pest deterrent device comprising: a sensor capable of detecting apest; a trigger circuit electrically coupled to the sensor, the triggercircuit providing a triggering signal having a first polarity inresponse to a triggering event, the trigger circuit activating a loadduring the triggering signal, the triggering signal being coupled to asumming junction through a capacitor as positive feedback; a negativefeedback path electrically coupling an inverse triggering signal to thesumming junction to discharge the capacitor and turn off the triggeringsignal and the load after a triggering period, the trigger circuitproviding a lockout signal following the triggering signal, the lockoutsignal being coupled to the summing junction through the capacitor aspositive feedback and an inverse lockout signal being coupled to thesumming junction as negative feedback to lock out the load until thelockout signal is turned off after a lockout period.
 2. The pestdeterrent device of claim 1 wherein the sensor produces both a positivepulse and a negative pulse upon detection of a pest, only one of thepositive pulse or the negative pulse triggering the load.
 3. The pestdeterrent device of claim 1 wherein the trigger circuit includes a firstamplifier providing a first output and a second amplifier providing asecond output, the first output being the inverse triggering signal andbeing coupled to an inverting input of the second amplifier, the secondoutput being the triggering signal.
 4. The pest deterrent device ofclaim 1 wherein the negative feedback path includes a resistor inparallel with a diode.
 5. The pest deterrent device of claim 4 whereinthe negative feedback path further includes a second resistor in serieswith the diode and in parallel with the resistor.
 6. A pest deterrentdevice comprising: a sensor capable of detecting a pest; a triggercircuit electrically coupled to the sensor, the trigger circuitproviding a triggering signal having a first polarity in response to atriggering event, the trigger circuit activating a load during thetriggering signal, the triggering signal being coupled from an output ofan inverting amplifier to a summing junction of a second invertingamplifier through a capacitor as positive feedback; a negative feedbackpath electrically coupling an inverse triggering signal from a secondoutput of the second inverting amplifier to the summing junction todischarge the capacitor and turn off the triggering signal and the load,the trigger circuit providing a lockout signal following the triggeringsignal, the lockout signal being coupled from the output of the firstinverting amplifier to the summing junction through the capacitor aspositive feedback and an inverse lockout signal being coupled from thesecond output of the second inverting amplifier to the summing junctionas negative feedback to lock out the load until the lockout signal isturned off.
 7. A method of locking out a detector circuit, the methodcomprising: providing a detection signal from the detector circuit to asaturation amplifier; producing a first saturated output signal from thesaturation amplifier, the first saturated output signal having a firstelectrical polarity; electrically coupling the first saturated outputsignal to an inverting input of a second amplifier; inverting the firstsaturated output signal to produce a triggering signal having a secondelectrical polarity and being configured to activate a load;electrically coupling the triggering signal through a capacitor to aninverting summing junction of the saturation amplifier; electricallycoupling the first saturated output signal to the inverting summingjunction of the saturation amplifier; discharging the inverting summingjunction to turn off the triggering signal and the load after a triggerperiod; producing a second saturated output signal from the saturationamplifier, the second saturated output signal having the secondelectrical polarity; inverting the second saturated output signal toproduce a lockout signal having the first electrical polarity and beingconfigured to de-activate the load; electrically coupling the lockoutsignal through the capacitor to the inverting summing junction of thesaturation amplifier; electrically coupling the second saturated outputsignal to the inverting summing junction of the saturation amplifier;discharging the inverting summing junction to turn off the lockoutsignal after a lockout period.
 8. The method of claim 7 wherein thelockout period is essentially equal to the trigger period.